Recently a car drove from the Canadian border in Washington state all the way down to the Mexican border in California. That's nearly 1,500 miles. What was amazing about the trip was the fact that the car burned only 12.4 gallons of fuel. The car got an average of 119 miles per gallon.

This was not a weird experimental car made out of tissue paper, with the driver lying in a prone position looking out through a periscope. This was a real, two-passenger car that looks pretty normal.

The car, called the Avion, proved once and for all that it is possible to create 100 miles-per-gallon cars that can drive on real roads under real conditions. What's even more amazing is the fact that the car was not created by a university research team or NASA scientists. The car was originally created in the 1980s by Craig Henderson and Bill Green and has been tweaked ever since.

It brings up a good question: How can our cars get more miles per gallon of fuel? Let's look at the different techniques that the Avion uses.

The most important feature of the Avion is its aerodynamics. Air flow has a huge effect on a car's fuel efficiency, especially at highway speeds. A typical car might need 10 to 20 horsepower to maintain a highway speed. The Avion needs far less horsepower -- down in the 3 to 4 horsepower range -- to achieve the same speeds.

The reason the Avion is so slippery is that it takes into account the major sources of drag in conventional cars and eliminates them. A big part of it is the shape of the rear of the car. Think about a raindrop.

It has a bulbous nose and a long, sloping tail. The longer tail is important, so the Avion's rear end looks a lot like a raindrop's.

The Avion is also a low car. Many of today's cars (especially SUVs and minivans) are taller than a person. That means the car has to move a lot of air out of the way as it goes down the road. The Avion is built like a low sports car, so there is less air to move.

In a conventional car, there are lots of extra sources of drag. The underside of a conventional car is all bumpy, with many extraneous pieces catching the wind. There is a big, vertical grill up front in most cars acting like a wall to the wind. Spoked wheels chop at the air. The Avion addresses all of these problems. It is low, has no grill, and has smooth hub caps and a smooth underside.

Another kind of drag comes from the rolling resistance of the tires. Big, fat tires with low air pressure create a lot of resistance. The Avion used low-resistance tires on its trip. Many hybrids are using these tires as well to improve their performance.

Another thing helping the Avion is its weight. It is made of aluminum and other lightweight materials so that it weighs half as much as a normal car. The weight helps whenever accelerating or going up a hill.

Think about the amount of energy needed to get a ping pong ball going 5 mph. Now compare that to the energy needed to get a bowling ball going the same speed. The ping pong ball requires the slightest touch. The bowling ball requires a big push. In a car, extra weight means extra fuel being burned every time you climb a hill.

And then there's the engine. The Avion uses a tiny diesel engine that is smaller than the engine found on many motorcycles. It doesn't need a giant engine because the car is so light and so slippery. The fact that it is a diesel also helps. Diesel fuel contains more energy than gasoline per gallon, so that helps right from the start. And a diesel engine uses a higher compression ratio, making it more efficient.

By putting all of these things together -- great aerodynamics, great tires, low weight and the most efficient engine possible -- it is possible to create a car with great mileage.